This invention relates to a method of and apparatus for detecting the presence of conductive particles in an oil flow system as, for example, in the lubricating system of internal combustion or jet engines and more particularly to such a method and apparatus adapted to give an indication of the quantity of such conductive particles present.
The presence of metal particles in the lubricating system of internal combustion or jet engines is not only harmful to such engines in operation but an increasing quantity of such particles is indicative of excessive wear of frictional surfaces of such engines. The detection of the presence of such particles and particularly of an increasing quantity of such particles will enable their removal both to prevent damage to the engine and for analysis in order to determine the condition of the engine. Since different frictional surfaces of the engine are made of different metals, it would be possible to detect a defect in a particular part of the engine such as the pistons, cylinders, bearing etc. by analysis of metal particles present in the oil flow of the lubricating system thereof upon detection of an increasing quantity of such particles.
Apparatus for this purpose heretofore proposed in the prior art has been based on the electrical sensing of metal particles as they pass through structures interposed in the oil flow and comprising spaced electrically conductive bodies or electrodes. For example, U.S. Pat. No. 2,349,992 to Schrader discloses various embodiments of such a device in which the presence of metal particles in the oil flow through the volume defined between spaced electrodes results in capacitive or resistive changes that are electrically sensed.
However, the electrodes of such devices must be physically close spaced from each other in order to provide the sensitivity required to detect minute metal particles distributed in the oil flow. The result is that such devices tend to act as fluid filters, collecting both metal particles and non-metallic contaminants. Thus, such devices tend to indicate the presence of an excessive quantity of metal particles, even under normal engine conditions, or to become clogged with non-metallic contaminants.
According to the teaching of U.S. Patent No. 3,457,504 to Arthur et al, an attempt is made to overcome the inherent problem described above by accenting the fluid filter characteristics of the device and decreasing the sensitivity of the electrical elements thereof. However, such an approach only tends to transfer the problem from the electrical elements to the filter element thereof since the relative condition of the filter element at any point in time will tend to determine the operating characteristics of the device. Thus, if the filter is made fine enough to trap the large quantity of minute particles of metal required to produce the desired electrical output, it will also trap a large quantity of non-metallic contaminants, thereby tending to reduce the oil flow therethrough and effectively deactivating the device for the purpose intended.
It is an object of this invention to provide an improved method and apparatus for detecting the presence and quantity of minute metal particles in an oil flow system.
It is another object of this invention to provide an improved method for detecting the presence and quantity of minute metal particles in an oil flow system without the use of fluid filter structures or inherent fluid filter action.
It is yet another object of this invention to provide improved apparatus for use in combination with a resistive type sensor in indicating the presence and quantity of conductive materials in an oil flow system.
It is a further object of this invention to provide an improved sensor element for use in such apparatus, which sensor element is highly sensitive to the presence of minute metal particles in such system but has no inherent fluid filtering characteristics.